The high pressure stator portions off a steam turbine also includes two envelopes constituted by the inner body and the outer body, together with a third envelope at the admission end when pressures and temperatures are very high.
Because of this multiplicity of envelopes, it is possible to reduce the differences of pressure and temperature between envelopes.
In addition, the inner and outer bodies are each made of two portions and are provided with flanges in the horizontal join plane to enable them to be bolted together.
The multiplicity of envelopes, and the presence of the horizontal joint plate flange for bolting-together the bodies lead:
to an increase in the transverse dimensions of the envelopes of the stator; and PA1 to said envelopes being non-isotropic.
This gives rise to an increase in forces and has an effect on the mechanical and thermal behavior of the envelopes and of their fastenings.
This problem is critical in the admission zone where pressure and temperature are very high.
In addition, for impulse steam turbines, the rotor is provided with disks supporting the moving blades, thereby considerably increasing the transverse dimensions of the bladed rotor, and consequently of the stator portions.